Crystal-Inspired Cellular Metamaterials and Triply Periodic Minimal Surfaces.

Triply periodic minimal surfaces (TPMSs) are found in many natural objects including butterfly wings, sea urchins, and biological membranes. They simultaneously have zero mean curvature at every point and a crystallographic group symmetry. A metamaterial can be created from such periodic surfaces or used as a reinforcement of a composite material. While a TPMS as a mathematical object has been known since 1865, only novel additive manufacturing (AM) technology made it possible to fabricate cellular materials with complex TPMS shapes. Cellular TPMS-based metamaterials have remarkable properties related to wetting/liquid penetration, shock absorption, and the absence of stress concentrators. Recent studies showed that TPMSs are also found in natural crystals when electron surfaces are considered. Artificial crystal-inspired metamaterials mimic such crystals including zeolites and schwarzites. These metamaterials are used for shock, acoustic waves, and vibration absorption, and as structural materials, heat exchangers, and for other applications. The choice of the crystalline cell of a material, as well as its microstructure, plays a decisive role in its properties. The new area of crystal-inspired materials has many common features with traditional biomimetics with models being borrowed from nature and adjusted for engineering applications.

Deposition of Nanostructured Tungsten Oxide Layers by a New Method: Periodic Modulation of the Deposition Angle.

Periodic modulation of the deposition angle (PMDA) is a new method to deposit nanostructured and continuous layers with controllable periodic density fluctuation. The method is used for the magnetron sputtering of a WO3 layer for an electrochromic device (ECD). An experimental study indicates that the electrochromic coloration-bleaching rate nearly doubles and the electrochromic efficiency grows by about 25% in comparison with the traditional method. The ECD efficiency rises with the increasing degree of nanostructure ordering, surface roughness, and homogeneity of the WO3 layer. The method is promising for coating deposition techniques needed to produce versatile devices with specific requirements for ion transport in surface layers, coatings, and interfaces, such as fuel cells, batteries, and supercapacitors.

Prediction of Cellular Structure Mechanical Properties with the Geometry of Triply Periodic Minimal Surfaces (TPMS).

The paper investigates the physical and mechanical properties of structures with the geometry of triply periodic minimal surfaces (TPMS). Test samples were made from polyamide using SLS (selective laser sintering) 3D printing technology, from polylactide using FDM (Fused deposition modeling) 3D printing technology, and from a photopolymer based on acrylates using LCD (liquid crystal display) technology; samples were made in the form of a cube with edge size 30 mm. The strength and energy-absorbing properties of TPMS-based cellular samples have been determined. To analyze the features of the geometry of the samples, the skeletal graph method was used. It is shown that this approach makes it possible to predict the physical and mechanical characteristics of products with TPMS geometry.

Reaction-Diffusion Pathways for a Programmable Nanoscale Texture of the Diamond-SiC Composite.

The diamond-SiC composite has a low density and the highest possible speed of sound among existing materials except for diamond. The composite is synthesized by a complex exothermic chemical reaction between diamond powder and liquid Si. This makes it an ideal material for protection against impact loading. Experiments show that a system of patterns is formed at the diamond-SiC interface. Modeling of reaction-diffusion processes of composite synthesis proves a formation of ceramic materials with a regular (periodic) interconnected microstructure in a given system. The composite material with interconnected structures at the interface has very high mechanical properties and resistance to impact since its fractioning is intercrystallite.

Improvement of vibrodamping properties of polyvinyl acetate-graphite composites by electron beam processing of the filler.

The effect of electron beam processing (energy 900 keV, absorbed dose in the range from 25 to 600 kGy) of graphite upon the efficiency of its use as a filler in polyvinyl acetate (PVA) based vibrodamping composites is studied. Graphite treatment at optimal doses above 200 kGy is found to provide a significant increase of damping loss factor for these composites at ambient and especially at elevated temperatures. The observed improvement of vibrodamping properties correlates with the increase in the content of Broensted centers (hydroxyl groups) on modified graphite surface probably due to the additional bonding of the filler particles with each other and PVA binder.

Alpha indirect conversion radioisotope power source.

Advantages of radioisotope-powered electric generators include long service life, wide temperature range operation and high-energy density. We report development of a long-life generator based on indirect conversion of alpha decay energy. Prototyping used 300 mCi Pu-238 alpha emitter and AlGaAs photovoltaic cells designed for low light intensity conditions. The alpha emitter, phosphor screens, and voltaic arrays were assembled into a power source with the following characteristics: Isc=14 microA; Uoc=2.3 V; power output -21 microW. Using this prototype we have powered an eight-digit electronic calculator and wrist watch.